1. Field of the Invention
The present invention relates to a method and an apparatus to control a disc drive, and more particularly, to a method of controlling and an apparatus to control a disc drive using an indirectly determined counter-electromotive force, which prevents collision and malfunction of a transducer and a disc by determining external vibrations and a magnitude of shock without installing an additional shock sensor in the disc drive.
2. Description of the Related Art
A hard disc drive includes a plurality of magnetic transducers which sense a magnetic field and magnetize a single rotating disc or each of a plurality of rotating discs to write and read information on and from the disc. In general, the information is formatted in a plurality of sectors in circular tracks. There is a number of tracks across each surface of a disc. Tracks located above each other on the plurality of rotating discs are grouped into cylinders. Therefore, each track is also defined by a cylinder.
In general, each of the transducers is integrated into a slider incorporated into a head gimbal assembly (HGA). Each HGA is attached to an actuator arm. The actuator arm has a voice coil adjacent to a certain magnetic assembly, together with a voice coil motor. In general, the hard disc drive includes a driving circuit which supplies current used to excite the voice coil motor, and a controller. The excited voice coil motor rotates the actuator arm and moves each of the transducers across surfaces of the discs.
When the information is written or read, there is a feasibility that the hard disc drive performs a seek routine when each of the transducers is moved from one cylinder to another cylinder. During the seek routine, the voice coil motor is excited by a current used to move each of the transducers to a new position on the surface of a disc. Also, the controller executes a servo routine on which each of the transducers is moved to an accurate position of a cylinder with respect to a center of a track.
The hard disc drive is very sensitive to disturbance caused by external shocks. As such, when the disturbance exceeds a tolerance range of the hard disc drive, a malfunction may occur, and when the disturbance is severe, a collision between a transducer and disc surface may occur such that the transducer or disc may be severely damaged.
A well-known technique of protecting a disc drive from disturbance is disclosed in U.S. Pat. No. 6,236,527 titled “Disk Drive with Actuator Load/Unload Controller.”
As shown in FIG. 1, the disc drive disclosed in U.S. Pat. No. 6,236,527 includes a shock sensor 140, a ramp 6 as a load/unload mechanism to load/unload a disc 1, A/D converters 130b and 140b which convert an analog signal into a digital signal, an actuator velocity detecting circuit 130a, a CPU 100 which determines and executes commands, a VCM driver 120 which drives an actuator, and a spindle driver 110 which drives a spindle motor 2 to rotate the disc 1. The disc drive also includes the actuator 3 as a position tracking driving unit to write and read data on and from the disc 1, a head/slider 4 that writes data on the disc 1 and reads data from the disc 1, and a VCM coil 5 which drives the actuator 3.
The head/slider 4 that writes and reads data on and from the disc 1 and the VCM coil 5 are both mounted in the actuator 3. The VCM coil 5, together with a permanent magnet (not shown), constitutes a voice coil motor (VCM). The VCM moves the actuator 3, and the spindle motor 2 rotates the disc 1. When the head/slider 4 is unloaded, the ramp 6 supports a head arm. The actuator 3, the VCM, and the ramp 6 constitute a load/unload mechanism that loads/unloads the head/slider 4 onto/from the disc 1. The spindle driver 110 drives the spindle motor 2 according to commands from the CPU 100.
A feature of the disc drive disclosed in the above U.S. Pat. No. 6,236,527 is that after a shock signal input to the disc drive is sensed using the shock sensor 140 during loading/unloading of the head/slider 4, if the value of the sensed shock signal exceeds a threshold, driving of the actuator 3 is stopped, and the head/slider 4 is unloaded by forced driving without control of velocity so that the disc drive is protected from external shocks.
According to the above related art, an additional sensor should be added to sense the magnitude of an outside shock, increasing costs of the disc drive. In addition, only in the loading/unloading mode is the disc drive protected from the external shocks, but the disc drive cannot be protected from smaller disturbance occurring in a high frequency region during the seek and track following modes.